1. Field of the Invention
This invention relates to measurement of relative phase proportions for single component fluids having multiple coexisting phases, and more particularly, to an apparatus and method for determining the quality of a steam-water mixture.
2. Description of the Prior Art
In large steam turbines and associated power generation equipment which have steam-water mixtures flowing therethrough it is highly desirable to obtain continuous quality measurements. Such quality measurements are necessary to determine thermodynamic performance and provide early warning indications of malfunctioning power generation equipment. Thermodynamic state points used to gauge turbine performance can be determined by temperature and pressure measurements when the steam is in the "dry" thermodynamic region. Thus, quality measurements of steam in fossil-fueled steam turbines are often necessitated only near the turbines' exhaust ends since the quality of the steam passing therethrough falls into the "wet" thermodynamic region only in the later, lower pressure stages of the turbines. Because nuclear-fueled steam turbines typically operate at lower pressures, wet steam is encountered in correspondingly earlier stages and thus require a more extensive number of quality determinations to accurately monitor their performance.
Previously, throttling and separating calorimeters were used to provide quality measurements on an intermittent or discrete time basis. However, calorimetry methods of quality measurement have recently fallen into disrepute and hence disuse because of serious questions raised as to the adequacy of the sampling procedures applied to the steam-water mixture. Since Pitot-type probes were often used to draw off samples of the steam-water mixture, radial traverses across the mixture were required to establish average qualities. More recently, in ASME Paper No. 72-WA/PTC-1 entitled "ASME Steam Turbine Code Test Using Radioactive Tracers", radioactive techniques have been set out as establishing steam quality. The results from such tests were also judged to be questionable since this method requires that elaborate safety precautions be taken in handling radioactive-decaying fluids, injecting them into the mixture, withdrawing samples of such fluids from the mixture at the point in question, and performing complex half-life calculations.
Disadvantages of all the previously mentioned quality measurement techniques include their inability to provide continuous quality monitoring and yield reliable quality determinations.